Spectroscopy of tetravalent chromium in different hosts in search for new, tunable, broad band lasers in the 1.2 um band

Spectroscopic studies are presented for cr4+ ions in different hosts. The crystals investigated in this work are divided into two categories. In the first category are included crystals containing chromium in the tetravalent state only. These are purely cr4+ doped crystals. The second category crystals are more complex, containing chromium in both tetravalent and trivalent states. Detailed investigations of the absorption and luminescence characteristics of cr4+ in cr4+:Y 2SiO5, which is a purely cr4+ doped crystal, allowed a better understanding to be achieved for the spectroscopic behavior of cr4+ in tetrahedral sites. Based upon these studies theoretical model has been developed for the near infrared fluorescence dynamics of the cr4+ ion. This model now explains many of the inconsistencies and uncertainties that existed in earlier work on cr4+ ion in the more complex crystals such as Cr:Mg2SiO4 and can serve as a standard model for future studies of cr4+ in other materials. Also, laser action in the near infrared was demonstrated for the first time in a purely cr4+ doped material, cr4+:Y2SiO5. This confirms the identification of cr4+ as the lasing center responsible for the near infrared laser action in cr4+ doped crystals. The effects of site symmetry and charge compensation on the spectroscopic behavior of cr4+ ions in tetrahedral sites have been taken into account in the present work. This has enabled a new systematic approach to be developed for the crystal field engineering of improved cr4+ laser materials